The present invention relates generally to sharing files amongst many users and more specifically to sharing geometric information and maintaining parametric consistency among elements in different software applications in a collaborative environment.
As is known in the art, there is a trend in the development of products having multiple components or subsystems to outsource the complete design of a component or an entire subsystem. In such a product development effort, therefore, different companies are designing different components or subsystems which must eventually be mechanically mated as assemblies to provide the final product.
As is also known, a product development effort typically requires multiple re-designs of each component prior to selecting a final product design. In the case where two or more components must be mated together, a mechanical or geometric change to one of the components may affect the ability of that component to mate with the other components. It may be necessary to change the other components so that all of the components are mechanically compatible. Thus, in this instance, a change to the geometry of one component can cause other components to change. This raises the problem of sharing design information between the different companies designing each of the components.
As is also known, design companies (referred to herein as suppliers since they are supplying a design) typically utilize Computer Aided Design (CAD), Computer Aided Manufacturing (CAM), Computer Aided Engineering (CAE), etc. software applications. When designing components and/or subsystems. Different companies often have different types of CAD, CAM, CAE and such applications are typically not compatible i.e. it is not possible to directly share parametrically editable data between the different software applications at the different companies and other software applications. Thus, when multiple companies are designing different components or subsystems, it can become relatively difficult, time consuming and burdensome to share information and maintain consistency during a re-design process.
Within large organizations such as automobile manufacturers, for example, a common approach for resolving interoperability issues has been to standardize the design process on a single CAD package. This makes it easier to share native CAD models with dedicated CAM and CAE packages. Assembly modeling is homogenous, since all the parts are coming in the same CAD format, and thus parametric control on the parts can be maintained within the assembly model. However, this strategy also has negative consequences. From a supplier viewpoint, it may require the adoption of new tools that may not best suit their design needs, and they are required to reveal native models to other suppliers or the Original Equipment Manufacturer (OEM), such native models may contain design history that may be proprietary to the supplier. From the OEM viewpoint, flexible competition amongst potential suppliers is restricted to those using the standardized tool set.
An alternative strategy relies upon the exchange of component and subsystem geometry between organizations through the use of neutral files. Initial Graphics Exchange Specification (IGES) is a neutral file format originated by the National Institute of Standards and Technology (NIST) and adopted by the American National Standards Institute (ANSI) to facilitate transfer of geometric data. In practice, IGES has become the standard in CAD/CAM data exchange in the U.S.
The International Organization for Standardization (ISO) has developed its own neutral file format commonly known as STEP (Standard for the Exchange of Product Model Data, standard number ISO-10303-21). The standard itself is more than a geometric description format, attempting to incorporate a complete definition of the physical and functional characteristics of a product across its entire life cycle, including design, manufacture and support. Application Protocols (APs) define subsets of the STEP standard. The AP most relevant to geometry (AP 203) is recognized by most major CAD and CAM systems, and is compatible with the Product Data Management (PDM) standards. Although parametric relations are not defined within AP 203, data translation tends to be more robust and require less rework than IGES files. STEP is now used internationally, particularly in the aerospace and defense sectors.
STEP and IGES are the most robust and accepted standards for transferring geometry between CAD systems. AutoCAD""s DXF (Data exchange Format) files have limited application and are not recognized as an official standard. VRML (Virtual Reality Modeling Language) is useful for visualization, but is not commonly used for importing geometry back into CAD systems. Similarly, STL (Standard Triangulated Language) files are appropriate for providing data to rapid prototyping devices, but do convert well between CAD systems. Although neutral files are not perfect, their relatively high level of functionality, ease of use, and acceptance by industry make them desirable as a means of transferring geometry between software applications, and in particular between CAD systems.
However, in a collaborative environment, the use of neutral files raises some issues related to content mapping, and to consistency maintenance of collections of elements. Content mapping is about associating the right low-level parametric geometric information within the neutral file, to the hi-level information as needed to maintain parametric consistency within the application or applications which uses the neutral file as a source of geometry. E.g. map the machined surface as represented within a CAM application to a specific surface stored in the neutral file. E.g. in assembly modeling, map the surfaces as defined in an assembly relation (e,g, a mating) to the right entities in the neutral file, or that the diameter of a bolt should match the diameter of a hole. Unless some automatic semantic interpretation capabilities are implemented within the application, content mapping is usually performed manually.
Consistency maintenance is about making sure that all the participants see an updated copy of the neutral file any time a change in the original native geometry has occurred. Geometry modifications can be classified as parametric changes to the model dimensions, or as changes to the model topology. Neither one is currently supported by any neutral file format. Changes to the topology (e.g. add/remove features) constitute a very hard problem for information sharing, and neutral file-based approaches are no exception to this.
Parametric changes are readily handled as long as they do not imply content re-mapping. Unfortunately, neutral file formats do not currently support parametric geometry, thus a new neutral representation is generated each time a parametric change occurs in the source geometry.
Manual generation and dissemination of updated neutral files is a viable option only for collaborative activities where geometric modifications are rare and easy-to-track events. Unfortunately this is not the case for most collaborative activities, thus the process needs to be automated to achieve a robust consistency control. Furthermore, the classical software architecture involving geometric information exchanges via neutral files allows only for parametric modifications driven by the original application that generated the geometric model. This unidirectional control flow is too limited for most collaborative environments: the capability of driving parametric geometry might be regarded as a valuable feature for the client applications that access the geometry through neutral files.
These considerations can be reformulated from the H-CAD (heterogenous CAD) viewpoint. Consider a heterogeneous assembly model built up from parts coming via neutral files created by different CAD applications. The proper mappings have been established to associate the assembly relations to the entities imported via neutral files, and only parametric changes to the part dimensions are allowed.
As any parametric change is performed to a part geometry, by any one of the part suppliers, new, up-to-date, neutral files are generated and sent over to the client application (the assembly modeler). Also, the latter must be notified to regenerate the overall assembly. If many changes like this one occur (which is common practice when exploring design alternatives), the risk of consistency loss is very high as there are many inter-relationships between elements and many neutral files to keep track of. Furthermore, in a traditional architecture based on neutral files, parametric changes can only be performed by the part designers. There is no way for the CAD assembly operator(s) to drive the parametric part geometry by himself or herself.
Each participant models a part, or subassembly, using its own CAD tools. In addition to exporting the resulting part geometry in the form of a neutral file, the participant provides (publishes) an Internet-enabled interface to allow remote users to drive a predefined set of parameters of his local model. The participant thus becomes an internet-enabled part server. The remote user, the client application, locates these services in a service marketplace and subscribes to them. Upon subscription, the client application receives a first copy of the geometry via a neutral file. As the client application needs to perform a parametric change to the imported geometry, it issues a parameter change request to the part server, through the services it had subscribed to. In response to the parameter change request the server recalculates its internal geometric model and sends back an updated copy of the neutral file.
The exchange of component and subsystem geometries between different CAD systems through the use of neutral files is referred to as a Heterogenous Assembly Modeling (HAM) process since different file formats are converted to the neutral file format. This approach is increasingly reliable, and overcomes the negative characteristics of tool standardization: allowing different organizations to use different tools; and protecting proprietary knowledge embedded within design history. However, one drawback of this approach consists in the loss of parametric control (i.e., the client using the neutral files cannot make parameter changes, such as dimension changes, to the native subsustystem CAD models maintained by suppliers. For example, in a HAM environment, the parametric control over the parts is lost as the parts are imported to the heterogeneous assembly via the neutral files.
In a collaborative environment, where many design variations are generated and evaluated, this drawback can reduce design flexibility and lead to slow component, subsystem and product iteration cycles between suppliers and the OEM. Some organizations are attempting to address this limitation by having suppliers provide discrete variations, but even so the inherent limitation remains.
Within the scope of designing assembled products, the problem of sharing product model geometric information is of fundamental importance not only for hybrid assembly modeling, but also for integrating assembly product modeling applications with assembly process modeling applications, such as CAAP (computer-aided Assembly Planning) applications. The reconstruction of assembly product geometry within process planning applications (a.k.a. virtual assemblies) can be of great help to manufacturing engineers to evaluate, determine, and select assembly operations, generate assembly/disassembly process plans, and visualize the results.
One approach to fulfill geometry information sharing needs is to incorporate all the information needed by different applications into a single, unified representation. For example, in the assembly field, some researchers feel that CAD system representations for assembled products should incorporate process data (i.e. assembly sequences) along with product data, and eventually CAE related data as well. However, most of the currently available CAD packages store assembly product information only in terms of product geometry, without incorporating process or CAE models, specifically, without incorporating information about the assembly process.
Another approach consists in defining geometric representations of the product which are suitable to be exchanged among applications, so that each application is provided with meaningful data to accomplish its task. Still other prior approaches have included interfacing assembly process modeling tools with CAD systems through neutral file-based and distributed object feature based techniques, or using Virtual Reality Modeling Language (VRML) or other neutral files to create virtual assembly environments.
Large product development firms have favored tool standardization to minimize information exchange problems. This centralized data management directive must come from a relatively dominant OEM. Automobile manufacturers are a good example of companies that typically use this strategy. However, as most supplier companies are also highly invested in their own CAD/CAM software, this forced standardization is often costly, unpopular, and creates barriers to the consideration of different suppliers.
It would, therefore, be desirable to provide a method of sharing and updating geometric information among different software applications in a collaborative environment, and to provide such a method such that it is usable by a large number of people at minimal cost and training.
A method for sharing geometric information amongst different software applications in a collaborative environment is presented. The method is based on geometric information sharing via neutral files, and incorporates Internet based messaging mechanisms amongst applications to maintain the parametric control over the exchanged geometry. In a preferred embodiment the proposed method is applied to Heterogeneous Assembly Modeling (HAM) system. By means of the presently disclosed method, within the heterogeneous assembly model, the parametric control over part geometry or assembly is maintained, even though the parts are imported in the assembly(ies) via neutral files originated by other CAD applications.